Post on 29-Apr-2022
1Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Chapter 7
Multiple Division Techniques
2Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
OutlineFrequency Division Multiple Access (FDMA)Time Division Multiple Access (TDMA)Code Division Multiple Access (CDMA)Comparison of FDMA, TDMA, and CDMAWalsh CodesNear-far ProblemTypes of InterferencesAnalog and Digital SignalsBasic 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)
3Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Frequency Division Multiple Access (FDMA)
User 1
User 2
User n
…
Time
Frequency
• Single channel per carrier
• All first generation systems use FDMA
4Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Time Division Multiple Access (TDMA)
Use
r 1
Use
r 2
Use
r n…
Time
Frequency
• Multiple channels per carrier
• Most of second generation systems use TDMA
5Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Code Division Multiple Access (CDMA)
Use
r 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 CDMAU
ser 2
Use
r nCode
...
6Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Types of Channels
Control channel Forward (Downlink) control channelReverse (Uplink) control channel
Traffic channelForward traffic (information) channel Reverse traffic (information) channel
7Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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
8Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
FDMA
MS #1
MS #2
MS #n
BS
f1’
f2’
fn’
f1
f2
fn
…
……
Reverse channels
(Uplink)
Forward channels
(Downlink)
9Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
FDMA: Channel Structure
1 2 3 … NFrequency
Total Bandwidth W=NWc
Guard Band Wg
4
Sub Band Wc
Frequency
Protecting bandwidth
…
f1’ f2’ fn’
…
f1 f2 fn
Reverse channels Forward channels
10Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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
11Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
TDMA: Channel Structure
… t
f #1 #2 #n #1 #2 #n…
(a). Forward channel
…#1 #2 #n
Frame FrameFrame
… t
f ’
#1 #2 #n #1 #2 #n…
(b). Reverse channel
…#1 #2 #n
Frame FrameFrame
12Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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
13Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
TDMA: Frame Structure (Cont’d)
…Time
Frequency#1 #2 #n #1 #2 #n… …#1 #2 #n
Frame FrameFrame
Head DataGuard time
14Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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
15Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Comparisons of FDMA, TDMA, and CDMA (Example)
222Control channels/cell
16.841Capacity vs FDMA320228/3=7657/3=19Voice calls/sector
333Sectors/cell8x40=32057x4=22857x1=57Voice channels/cell
40**4*1Calls per RF channel85757Usable channels/cell
12.5/1.25=10416/7=59416/7=59Channels/cell12.5/1.25=1012.5/0.03=41612.5/0.03=416No. of RF channels
1.25 MHz0.03 MHz0.03 MHzRequired channel BW177Frequency reuse
12.5 MHz12.5 MHz12.5 MHzAllocated BandwidthCDMATDMAFDMAOperation
* Depends on the number of slots ** Depends on the number of codes
16Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Digital signal s(t)
Code c(t)
Spreading signal m(t)
Code c(t)
Digital signal s(t)
Spreading De spread
Frequency Frequency Frequency
Power Power Power
Transmitter Receiver
Concept of Direct Sequence Spread Spectrum
17Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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
18Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Time
Frequency
An Example of Frequency Hopping Pattern
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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
20Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
MS1MS2 BS
Distance Distance0
d2 d1
Received signal strength
MS1MS2 BS
Near-far Problem
21Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Frequency
Baseband signal
Frequency
Interference baseband signals
Spreading signal
Frequency
Despread signal
Interference signals
Interference in spread spectrum system
Types of Interference
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Adjacent Channel Interference
f1 f2
MS1 MS2
Frequency
Power
23Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Power Control
Pr Pt =
1
4πdf
cα
Controlling transmitted power affects the CIR
Pt = Transmitted powerPr = Received power in free spaced = Distance between receiver and transmitterf = Frequency of transmissionc = Speed of lightα = Attenuation constant
24Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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 antennaLimit noise and interference, e.g., FM (Frequency Modulation)Multiplexing techniques,
e.g., FDM, TDM, CDMA
25Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Analog and Digital SignalsAnalog Signal (Continuous signal)
Digital Signal (Discrete signal)
Time
Amplitude
Time
Amplitude
1 1 1 10 0
Bit
+
_0
0
S(t)
26Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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..
27Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Amplitude Modulation (AM)
Message signalx(t)
Carrier signal
AM signals(t)
Amplitude of carrier signal is varied as the message signal to be transmitted.
Frequency of carrier signal is kept constant.
Time
Time
Time
28Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
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 signalx(t)
FM signal s(t)
Time
Time
Time
29Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Frequency Shift Keying (FSK)
• 1/0 represented by two different frequencies slightly offset from carrier frequency
Message signalx(t)
Carrier signal 2for binary ‘0’
Carrier signal 1for binary ‘1’
FSK signals(t)
1 0 1 1 0 1
Time
Time
Time
Time
30Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
Phase Shift Keying (PSK)• Use alternative sine wave phase to encode bits
Carrier signal
Carrier signal)2sin( ππ +tfc
Message signalx(t)
)2sin( tfcπ
1 0 1 1 0 1
PSK signals(t)
Time
Time
Time
Time
31Copyright © 2002, Dr. Dharma P. Agrawal and Dr. Qing-An Zeng. All rights reserved.
QPSK Signal Constellation
Q
I0,01,1
0,1
1,0
Q
I01
(a) BPSK (b) QPSK
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All Possible State Transitions in π/4 QPSK
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Quadrature Amplitude Modulation (QAM)
Combination of AM and PSKTwo carriers out of phase by 90 deg are amplitude modulated
Rectangular constellation of 16QAM
I
Q
0000010011001000
0001010111011001
0011011111111011
0010011011101010