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Chapt-07.ppt
1.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 1 Chapter 7 Multiple Division Techniques
2.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 2 Outline Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA) Comparison of FDMA, TDMA, and CDMA Walsh Codes Near-far Problem Types of Interferences Analog and Digital Signals Basic Modulation Techniques Amplitude Modulation (AM) Frequency Modulation (FM) Frequency Shift Keying (FSK) Phase Shift Keying (PSK) Quadrature Phase Shift Keying (QPSK) Quadrature Amplitude Modulation (QAM)
3.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 3 Frequency Division Multiple Access (FDMA) User 1 User 2 User n … Time Frequency • Single channel per carrier • All first generation systems use FDMA
4.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 4 Time Division Multiple Access (TDMA) User 1 User 2 User n … Time Frequency • Multiple channels per carrier • Most of second generation systems use TDMA
5.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 5 Code Division Multiple Access (CDMA) User 1 Time Frequency • Users share bandwidth by using code sequences that are orthogonal to each other • Some second generation systems use CDMA • Most of third generation systems use CDMA User 2 User n Code . . .
6.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 6 Types of Channels Control channel Forward (Downlink) control channel Reverse (Uplink) control channel Traffic channel Forward traffic (traffic or information) channel Reverse traffic (traffic or information) channel
7.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 7 Types of Channels (Cont’d) MS BS f1’ f2’ fn’ f ’ f … Reverse channel (Uplink) Forward channels (Downlink) f1 f2 fn … Control channels Traffic channels
8.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 8 FDMA MS #1 MS #2 MS #n BS f1’ f2’ fn’ f1 f2 fn … … … Reverse channels (Uplink) Forward channels (Downlink)
9.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 9 FDMA: Channel Structure 1 2 3 … N Frequency Total Bandwidth W=NWc Guard Band Wg 4 Sub Band Wc Frequency Protecting bandwidth … f1’ f2’ fn’ … f1 f2 fn Reverse channels Forward channels
10.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 10 MS #1 MS #2 MS #n BS … … Reverse channels (Uplink) Forward channels (Downlink) t Frequency f ’ #1 … #1 … Frame Slot … #1 … #1 Frame … t Frequency f Frame Frame … t #2 … #2 … … t #n … #n … … #2 … #2 … t … #n … #n … t TDMA
11.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 11 TDMA: Channel Structure … t f #1 #2 #n #1 #2 #n … (a). Forward channel … #1 #2 #n Frame Frame Frame … t f ’ #1 #2 #n #1 #2 #n … (b). Reverse channel … #1 #2 #n Frame Frame Frame
12.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 12 TDMA: Frame Structure (Cont’d) … Time Frequency f = f ’ #1 #2 #n #1 #2 #n … Forward channel Reverse channel … #1 #2 #n Forward channel Frame Frame #1 #2 #n … Reverse channel Channels in Simplex Mode
13.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 13 TDMA: Frame Structure (Cont’d) … Time Frequency #1 #2 #n #1 #2 #n … … #1 #2 #n Frame Frame Frame Head Data Guard time
14.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 14 Code Division Multiple Access (CDMA) MS #1 MS #2 MS #n BS C1’ C2’ Cn’ C1 C2 Cn … … … Reverse channels (Uplink) Forward channels (Downlink) Frequency f ’ Note: Ci’ x Cj’ = 0, i.e., Ci’ and Cj’ are orthogonal codes, Ci x Cj = 0, i.e., Ci and Cj are orthogonal codes Frequency f
15.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 15 Comparisons of FDMA, TDMA, and CDMA (Example) Operation FDMA TDMA CDMA Allocated Bandwidth 12.5 MHz 12.5 MHz 12.5 MHz Frequency reuse 7 7 1 Required channel BW 0.03 MHz 0.03 MHz 1.25 MHz No. of RF channels 12.5/0.03=416 12.5/0.03=416 12.5/1.25=10 Channels/cell 416/7=59 416/7=59 12.5/1.25=10 Control channels/cell 2 2 2 Usable channels/cell 57 57 8 Calls per RF channel 1 4* 40** Voice channels/cell 57x1=57 57x4=228 8x40=320 Sectors/cell 3 3 3 Voice calls/sector 57/3=19 228/3=76 320 Capacity vs FDMA 1 4 16.8 * Depends on the number of slots ** Depends on the number of codes Delay ? ? ?
16.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 16 Digital signal s(t) Code c(t) Spreading signal m(t) Code c(t) Digital signal s(t) Spreading Despread Frequency Frequency Frequency Power Power Power Transmitter Receiver Direct Sequence Spread Spectrum for CDMA
17.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 17 Digital signal Hopping Pattern Spreading signal Digital signal Spreading Despread Frequency Frequency Frequency Power Power Power Hopping Pattern Transmitter Receiver Concept of Frequency Hopping Spread Spectrum
18.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 18 Time Frequency An Example of Frequency Hopping Pattern
19.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 19 Walsh Codes (Orthogonal Codes) Wal (0, t) t Wal (1, t) t Wal (2, t) t Wal (3, t) t Wal (4, t) t Wal (5, t) t Wal (6, t) t Wal (7, t) t
20.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 20 MS1 MS2 BS Distance Distance 0 d2 d1 Received signal strength MS1 MS2 BS Near-far Problem
21.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 21 Frequency Baseband signal Frequency Interference baseband signals Spreading signal Frequency Despread signal Interference signals Interference in spread spectrum system in CDMA Types of Interference in CDMA
22.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 22 Adjacent Channel Interference in CDMA f1 f2 Channel1 Channel2 Frequency Power
23.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 23 Power Control in CDMA Pr Pt = 1 4df c Controlling transmitted power affects the CIR Pt = Transmitted power Pr = Received power in free space d = Distance between receiver and transmitter f = Frequency of transmission c = Speed of light = Attenuation constant (2 to 4)
24.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 24 Modulation Why need modulation? Small antenna size Antenna size is inversely proportional to frequency e.g., 3 kHz 50 km antenna 3 GHz 5 cm antenna Limits noise and interference, e.g., FM (Frequency Modulation) Multiplexing techniques, e.g., FDM, TDM, CDMA
25.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 25 Analog and Digital Signals Analog Signal (Continuous signal) Digital Signal (Discrete signal) Time Amplitude Time Amplitude 1 1 1 1 0 0 Bit + _ 0 0 S(t)
26.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 26 Hearing, Speech, and Voice-band Channels Voice-grade Telephone channel Human hearing Human speech Frequency (Hz) Frequency (Hz) Pass band Frequency cutoff point Guard band Guard band 100 0 200 3,500 4,000 10,000 ..
27.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 27 Amplitude Modulation (AM) Message signal x(t) Carrier signal AM signal s(t) Amplitude of carrier signal is varied as the message signal to be transmitted. Frequency of carrier signal is kept constant. Time Time Time
28.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 28 Frequency Modulation (FM) FM integrates message signal with carrier signal by varying the instantaneous frequency. Amplitude of carrier signal is kept constant. Carrier signal Message signal x(t) FM signal s(t) Time Time Time
29.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 29 Frequency Shift Keying (FSK) • 1/0 represented by two different frequencies slightly offset from carrier frequency Message signal x(t) Carrier signal 2 for message signal ‘0’ Carrier signal 1 for message signal ‘1’ FSK signal s(t) 1 0 1 1 0 1 Time Time Time Time
30.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 30 Phase Shift Keying (PSK) • Use alternative sine wave phase to encode bits Carrier signal Carrier signal ) 2 sin( t fc Message signal x(t) ) 2 sin( t fc 1 0 1 1 0 1 PSK signal s(t) Time Time Time Time
31.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 31 QPSK Signal Constellation Q I 0,0 1,1 0,1 1,0 Q I 0 1 (a) BPSK (b) QPSK
32.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 32 All Possible State Transitions in /4 QPSK
33.
Copyright © 2003,
Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved. 33 Quadrature Amplitude Modulation (QAM) Combination of AM and PSK Two carriers out of phase by 90 deg are amplitude modulated Rectangular constellation of 16QAM I Q 0000 0100 1100 1000 0001 0101 1101 1001 0011 0111 1111 1011 0010 0110 1110 1010
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