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Chapter 3. Wireless Systems: Multiple Access Technologies & Standards. FDMA. Power. Frequency. Time. TDMA. Power. Frequency. Time. CDMA. Power. Frequency. Time. Multiple Access Technologies. FDMA (example: AMPS) Frequency Division Multiple Access

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Chapter 3

Wireless Systems:

Multiple Access Technologies & Standards

RF100 (c) 1998 Scott Baxter


Multiple access technologies

FDMA

Power

Frequency

Time

TDMA

Power

Frequency

Time

CDMA

Power

Frequency

Time

Multiple Access Technologies

  • FDMA (example: AMPS)

    Frequency Division Multiple Access

    • each user has a private frequency (at least in their own neighborhood)

  • TDMA (examples: IS-54/136, GSM)

    Time Division Multiple Access

    • each user has a private time on a private frequency (at least in their own neighborhood)

  • CDMA (examples: IS-95, J-Std. 008)

    Code Division Multiple Access

    • users co-mingle in time and frequency but each user has a private code (at least in their own neighborhood)

RF100 (c) 1998 Scott Baxter


Conventional technologies recovering the signal avoiding interference

AMPS-TDMA-GSM

1

1

4

7

2

6

7

3

5

6

1

4

5

1

2

4

1

7

2

3

6

3

5

1

1

Conventional Technologies:Recovering the Signal / Avoiding Interference

  • In ordinary radio technologies, the desired signal must be stronger than all interference by at least a certain margin called C/I (carrier-to-interference ratio)

    • the type of signal modulation determines the amount of interference which can be tolerated, and thus the required C/I

  • In conventional systems, the C/I is controlled mainly by the distance between co-channel cells

    • frequency usage is planned so that co-channel users don’t have interference worse than C/I

    • any undesired interference we face is coming from the nearest co-channel cells, far away

    • if the signal is delicate, then we need a big C/I and the co-channel cells must be very far away

    • if the signal is more rugged, we can tolerate more interference (smaller C/I) allowing the co-channel cells a bit closer without bad effects

Figure of Merit: C/I

(carrier/interference ratio)

AMPS: +17 dB

TDMA: +14 to 17 dB

GSM: +7 to 9 dB.

RF100 (c) 1998 Scott Baxter


B

D

A

C

Tech-nology

Modulation

Type

Channel Bandwidth

Quality Indicator

D

C

B

A

Sites

AMPS

Analog FM

30 kHz.

C/I @ 17 dB

NAMPS

Analog FM

10 kHz.

C/I @ 17 dB

TDMA

DPQSK

30 kHz.

C/I @ 17 dB

-50

GSM

GMSK

200 kHz.

C/I @ 7-9 dB

RSSI, dBm

CDMA

QPSK/OQPSK

1,250 kHz.

Eb/No @ 6dB

C/I

-120

Handoffs and C/I

  • One purpose of handoff is to keep the call from dropping as the mobile moves out of range of individual cells

  • Another purpose of handoff is to ensure the mobile is using the cell with the best signal strength and best C/I at all times

  • Notice in the signal graphs at lower right how the mobile’s C/I is maintained at a usable level as it goes from cell to cell

RF100 (c) 1998 Scott Baxter


Cdma using a new dimension

CDMA

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 a new dimension, CODING, to discriminate between users

    • In CDMA, we do not try to immediately recover the pulses of energy from each user. Instead, we watch long groups of the totals of everybody’s pulses, and detect little patterns which are the “signature” of the user we wish to decode

  • In CDMA, the interference originates mainly from nearby users in the same general area

  • Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code

Figure of Merit: C/I

AMPS: +17 dB

TDMA: +14 to +17 dB

GSM: +7 to 9 dB.

CDMA: -10 to -17 dB.

Although the CDMA C/I is negative, the decoding process recovers the user’s energy while discarding others’ energy. The final net result is Eb/No, typically about +6 db.

We’ll study this in detail later.

RF100 (c) 1998 Scott Baxter


Wireless technologies a summary major technologies deployed in north america

Technology

StandardsDocuments

FirstUsed

Modul-ation

ServiceTypes

Band-width

Users/Carrier

AMPSAdvanced Mobile Phone Service

EIA/TIA 553IS-19 mobileIS-20 base sta.

1983

AnalogFM17 dB C/I

Voice

30 kHz

1

NAMPS

Narrowband AMPS

IS-88

1990

AnalogFM17 dB C/I

VoiceSMS

10 kHz

1

D-AMPS

Digital AMPSNorth American TDMA

IS-54B

1993

DigitalDQPSK14 dB C/I(fragile)

VoiceData

30 kHz

3(6 in future?)

IS-136

1995

+CAVE

+DCCH

+SMS

GSM

European 2nd-Generation TDMA

ETSI/TIA/ITUmultipledocuments

1992

DigitalGMSK6 dB C/I(robust)

VoiceSMSCell Bcstfrq hop’g

200 kHz

8(16 in future?)

CDMACode Division Multiple Access

IS-95A,

Joint Std. 008,+ features stds

1995

DigitalQPSKSpreadSpectrum

VoiceSMSData+more

1250 kHz

22 8kb17 13kb

Wireless Technologies: A SummaryMAJOR TECHNOLOGIES DEPLOYED IN NORTH AMERICA

RF100 (c) 1998 Scott Baxter


Summary of major global analog wireless technologies
Summary of Major Global Analog Wireless Technologies

AMPS

IS-553

NAMPS

IS-91

TACS

NMT450

NMT900

C-450

Frequency Band

800

800

900

450

900

450

Channel Spacing

30 kHz.

10 kHz.

25

25

12.5

20

Speech Modulation

FM

FM

FM

FM

FM

FM

Freq. Deviation

12 kHz.

5 kHz.

9.5

5.0

5.0

4.0

Signaling Modulation

Dir.FSK

Dir.FSK

Dir.FSK

Aud.FFSK

Aud.FFSK

Dir.FSK

Signaling Bit Rate

10 kb/s

10 kb/s

8 kb/s

1200 b/s

1200 b/s

5280 b/s

Overlay Signaling?

no

no

no

no

no

yes

Paging/Access

CCH (f)

CCH (f)

CCH (f)

CCH (f)

CCH (f)

CCH (f)

In-Call Supervision

SAT

DSAT

SAT

?

?

overlay

In-Call Control

ST

DSAT

ST

?

?

overlay

Call Control

ST

DSAT

ST

?

?

overlay

Handoff Logic

BTSLCR

BTSLCR

BTSLCR

BTSLCR

BTSLCR

BTSLCR

RF100 (c) 1998 Scott Baxter


Summary of major global digital wireless technologies

GSM, DCS1800 PCS1900

D-AMPS

IS-54

IS-136

CDMA

IS-95

JStd008

Japan PDC

CT-2

DECT

Access Method

TDMA

TDMA

CDMA

TDMA

TDMA

TDMA

Frequency Band(s)

900

1800

1900

800

1900*

800

1900

8/900

1400

865

1880

Channel Spacing

200

30, 50*

x

50/25i

100

1728

Modulation type

GMSK

DQPSK

QPSK

DQPSK

GFSK

GFSK

Signal Bandwidth

200+

30

1250+

50

100

1800

Signaling Modulation

GMSK

DQPSK

QPSK

DQPSK

GFSK

GFSK

Transmission, kb/s

~240

~44

1229ss

42

72

1152

Paging/Access ch.

CCH (t)

CCH(f)

CCH(c)

CCH(f)

BCH

BCH

Signaling kb/s

~30

~44

9.6

x

32

32

Info kb/s

14.4

x

9.6,14.4

11.2

32

32

Info frames/s

~200

50

50

50

packets

100

In-Call signaling

TCH,

SDCCH

TCH,

SACCH

TCH

ACCH

SACCH

hybrid

hybrid

Handoff Logic

MAHO

MAHO+

MDHO

?

?

MDHO

Summary of Major Global Digital Wireless Technologies

RF100 (c) 1998 Scott Baxter


Wireless system capacity

AMPS, D-AMPS, N-AMPS

2

1

3

1 Users

3

7

1

6

4

5

Vulnerability:

C/I @ 17 dB

30

30

10 kHz Bandwidth

Typical Frequency Reuse N=7

2

Vulnerability:

C/I @ 6.5-9 dB

1

8 Users

3

4

200 kHz

Typical Frequency Reuse N=4

1

CDMA

Vulnerability:

EbNo@ 6 dB

1

1

1

1

1

1

1

22 Users

1

1

1

1

1

1

1250 kHz

Typical Frequency Reuse N=1

Wireless System Capacity

Each wireless technology (AMPS, NAMPS, D-AMPS, GSM, CDMA) uses a specific modulation type with its own unique signal characteristics

  • Signal Bandwidth determines how many RF signals will “fit” in the operator’s licensed spectrum

  • Robustness of RF signal determines tolerable level of interference and necessary physical separation of cochannel cells

  • Number of users per RF signal directly affects capacity

  • In the following page, we will develop the number of users and traffic in erlangs per site for each of the popular wireless technologies

RF100 (c) 1998 Scott Baxter


Comparison of wireless system capacities
Comparison of Wireless System Capacities

RF100 (c) 1998 Scott Baxter


Capacity of multicarrier cdma systems

CDMA Carrier Frequencies

1

2

3

4

5

6

7

8

9

10

11

f

Capacity of Multicarrier CDMA Systems

RF100 (c) 1998 Scott Baxter


End of section
End of Section

RF100 (c) 1998 Scott Baxter


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