close

Вход

Забыли?

вход по аккаунту

?

Wireless Networks - book

код для вставкиСкачать
Wireless Networks
Ivan Marsic
Rutgers University
1
ISO OSI Protocol Stack
• Protocol at layer i doesn’t know about protocols
at iпЂ­1 and iпЂ«1
Application
4: Transport
• Reliable (TCP)
• Unreliable (UDP)
3: Network
• End-to-end (IP)
• Routing
• Address resolution
2: Link
• IEEE 802.11 WiFi
• IEEE 802.3 Ethernet
• PPP (modems, T1)
1: Physical
MAC
• Radio spectrum
• Infrared
• Fiber
• Copper
2
Infrastructure vs. Ad Hoc (1)
(a)
(b)
3
Infrastructure vs. Ad Hoc (2)
(c)
(d)
4
Waves
5
1 KHz
1 MHz
LF
30 KHz
1 GHz
(AM radio)
MF
300 KHz
UV
Visible
Infrared
EM Spectrum Allocation
1 THz
X rays
1 PHz
1 EHz
(SW radio) (FM radio - TV) (TV – Cell.)
HF
VHF
UHF
3 MHz
30 MHz
300 MHz
ISM
902 MHz
Gamma
rays
928 MHz
Cordless phones
Baby monitors
(old) Wireless LANs
2.4 GHz
2.4835 GHz
IEEE 802.11b, g
Bluetooth
Microwave ovens
Freq.
SHF
30 GHz
Freq.
5.785 GHz
Freq.
3 GHz
UNII
5.725 GHz
IEEE 802.11a
HiperLAN II
6
Communication Process
Information
Source
Communication
Channel
Transmitter
Receiver
Destination
Noise
Source
Source
Data:
0 1 0 0 1 1 0 0 1 0
Input
Signal:
S
Noise:
N
Output
Signal:
S+N
Sampling
Times:
Source
Data:
Decision
threshold
0 1 0 0 1 1 0 0 1 0
Data
1 1 0 0 1 1 1 0 1 0
Received:
Bits in error
7
Decibel definition
Power in
Link,
channel,
repeater, or
node
Power out
8
Three dots running
at the same speed
around the circle in
different lanes:
Displacement
Fourier Series Approximation
Resultant
Time
60п‚°
90п‚°
30п‚°
180п‚°
0п‚°
60п‚°
30п‚°
120п‚°
90п‚°
150п‚°
240п‚°
210п‚°
300п‚°
270п‚°
360п‚°
330п‚°
Angular phase of fundamental wave
9
Phase Space
Phase space:
Amplitude
пЃ°/2
Period (T)
Frequency пЃ· = 2пЃ° / T
A
пЃ· [rad / s]
A
Time (t)
пЃЄ
0
2пЃ°
пЃ°
Phase (пЃЄ)
A пѓ— sin (пЃ· пѓ— t пЂ« пЃЄ)
3пЃ° / 2
10
Wireless Transmission and
Receiving System
Modulator
Demodulator
Error Control
Encoder
Error Control
Decoder
Source Encoder
(Compress)
Source Decoder
(Decompress)
Information
Source
Destination
Receiver
Transmitter
Communication
Channel
11
Modulation
C a rrie r sig n a l
C a rrie r sig n a l
A n a lo g m e ssa g e sig n a l
D ig ita l m e ssa g e sig n a l
1
0
1
1
0
A m p litu d e -m o d u la te d (A M ) sig n a l
A m p litu d e -sh ift-ke yin g (A S K ) sig n a l
F re q u e n cy -m o d u la te d (F M ) sig n a l
F re q u e n cy -sh ift-ke yin g (F S K ) sig n a l
P h a se -m o d u la te d (P M ) sig n a l
P h a se -sh ift-ke yin g (P S K ) sig n a l
12
Modulation—PSK
01
010
011
135п‚°
90п‚°
10
90п‚°
0п‚°
00
100
11
0011
0101
0100
0000
0001
1001
1000
1100
1101
1011
1010
1110
1111
000
270п‚° 315п‚°
101
(a)
0010
001
225п‚°
270п‚°
0110
45п‚°
180п‚°
180п‚°
0111
111
(b)
(c)
110
00
01
135п‚°
45п‚°
225п‚°
10
315п‚°
11
13
Amplitude
Example 2.1
3 bits
3 bits
3 bits
110
100
010
Time
14
Gaussian r.v. and Q-function
p (x)
1 0 пЂ­0
F (x)
Q (z)
1
1 0 пЂ­1
1
пЃі
пЃі пѓ– (2 пЃ° )
ВЅ
x
0
x
пЃ­
1 0 пЂ­2
пЃ­
0
(a)
(b)
1 0 пЂ­3
p (x)
1 0 пЂ­4
P r{x п‚і z}
1 0 пЂ­5
x
(c)
0
z
(d)
z
1 0 пЂ­6
0
1
2
3
4
15
Effect of Noise on Signal
C hannel
b its (sym b o ls) in
M
torr
lato
Moodduula
+
b its (sym b o ls) o u t
DDeem
torr
lato
moodduula
D e c is io n d e vice
B it-to -w a ve fo rm
m apper
N o ise pd f
NNooise
,пЃі))
(0,пЃі
ise ~~ NN(0
(a)
S ym b o l A
пЂ«
VA
D e cisio n
th re sh o ld
P (A R |B T )
0
P (B R |A T )
VB
(b)
S ym b o l B
пЂ­
16
Probability of Error for
2,4-PSK
P ro b a b ility o f b it e rro r, P e
1 0 пЂ­1
1 0 пЂ­2
QPSK
1 0 пЂ­3
BPSK
1 0 пЂ­4
1 0 пЂ­5
1 0 пЂ­6
1 0 пЂ­7
0
2
4
6
8
10
12
14
S N R p e r b it, E b /N 0 (d B )
17
Discrete vs. Continuous Channel
Source
0 1 0 0 1 1 0 0 1 0
Data:
(0 ,0 ,1 )
(1 ,1 ,1 )
(1 ,0 ,1 )
Input
Signal:
Noise:
(1 ,0 ,0 )
Output
Signal:
(a)
(b)
(c)
18
Signals as Vectors
s(t)
Example 3-bit message:
1 0 1
5V
t
T
A three-bit signal waveform
(a)
p1(t)
(пЂ­1,пЂ­1,1)
(1,1,1)
(1,пЂ­1,1)
p2(t)
s1(t)
(пЂ­1,1,1)
(0,0,0)
(пЂ­1,1,пЂ­1)
p3(t)
s2(t)
0 T 2T 3T
(b)
s3(t)
Orthogonal function set (Basis vectors)
(c)
(1,пЂ­1,пЂ­1)
(1,1,пЂ­1)
(d)
19
Geometric Representation
пЂ­1,пЂ­1,1
пЂ­1,1
1,1
N
1,пЂ­1,1
пЂ­1
S
1
S
пЂ­1,пЂ­1
(a)
(b)
N
1,пЂ­1
111
S
rS = пѓ–2
N
пЂ­1,1,1
пЂ­1,пЂ­1,пЂ­1
пЂ­1,1,пЂ­1
rN= 1/пѓ–2
(c)
1,пЂ­1,пЂ­1
1,1,пЂ­1
20
Signal Space
N
SR
ST
(a)
2 BT ( S пЂ« N )
(b)
21
Locus of Error-Causing Signals
SR = ST + N
O'
N
h
Noise sphere,
radius 2 BTN ,
centered on ST
2h
ST
O'
O
(a)
Signal sphere,
radius 2 BTS
(b)
22
Error Detection and Correction
пЂ­ 1 ,пЂ­ 1 ,1
пЂ­1,1
пЂ­ 1 ,1 ,1
1 ,пЂ­ 1 ,1
Error
message 1,1
111
r3 = 2 пѓ– 3
Valid
message
1 ,пЂ­ 1 ,пЂ­ 1
r2 = 2 пѓ– 2
r1 = 2
Error
message
1 ,1 ,пЂ­ 1
пЂ­1,пЂ­1
(a)
1,пЂ­1
Valid
message
(b)
23
Wave Interactions
R o u g h ce ilin g
s1
(a)
R e ce ive r 1
T ra n sm itte r
s 0 + s 1' + s 2'
s0
s
s2
“K n ife -e d g e ”
o b sta cle
R e ce ive r 2
s 1 '' + s 2 ''
(b)
24
Interference & Doppler Effect
s0
s1
s2
v
s 0+ s 1+ s 2
(a)
(b)
25
Multipath Fading (1)
T ra n s m itte d
s ig n a l
T ra n s m itte d
s ig n a l
R e ce ive d
N L O S s ig n a ls
R e ce ive d
L O S sig n a l
R e ce ive d
L O S sig n a l
T im e
R e ce ive d
N L O S s ig n a ls
T im e
26
Plane-Earth Model
R e c e iv e r
R e c e iv e r
S o u rce
S o u rce
(a)
(b)
27
Delay Spread
пЃґ1
Tx
Rx
P a th p ow er (d B )
пЃіпЃґ
пЃґ2
пЃ­пЃґ
пЃґ m xd
D e la y (s)
пЃґ0
(a)
пЃґ1
пЃґ2
пЃґ3
пЃґ4
пЃґ5
пЃґ6
(b)
28
Discrete-time Delay Model
пЃ„пЃґ
ЕЎ(t)
п‚ґ
g (t, 0 )
пЃ„пЃґ
п‚ґ
пЂ«
g (t, пЃ„ пЃґ)
пЃ„пЃґ
п‚ґ
пЂ«
g (t, 2 пЃ„ пЃґ)
пЃ„пЃґ
п‚ґ
пЂ«
g (t, 3 пЃ„ пЃґ)
п‚ґ
g (t, N пЃ„ пЃґ)
пЂ«
r(t)
29
Multipath Fading (2)
Delay spread (2 components)
Flat Fading
Direct path (1 component)
0 .2
0.15
0 .1 5
0.1
0 .1
0.05
0 .0 5
0
0
пЂ­0.05
пЂ­ 0 .0 5
пЂ­0.1
пЂ­ 0 .1
0
0.5
1.0
1.5
2.0
2.5
3.0
0
0 .5
1 .0
1 .5
2 .0
2 .5
3 .0
Doppler spread (2 components)
Fast Fading
0 .2
Delay spread (2 components)
Frequency Selective Fading
0 .1 5
0 .1
0 .1
0 .0 5
0 .0 5
0
0
пЂ­ 0 .0 5
пЂ­ 0 .0 5
0
0 .5
1 .0
1 .5
2 .0
2 .5
3 .0
30
0
0 .5
1 .0
1 .5
2 .0
2 .5
3 .0
Error Probabilities
P ro b a b ility o f b it e rro r, P e
1 0 пЂ­0
1 0 пЂ­1
BPSK
R a yle ig h
1 0 пЂ­2
1 0 пЂ­3
BPSK
AW GN
1 0 пЂ­4
1 0 пЂ­5
0
2
4
6
8
10
12
14
16
18
20
S N R p e r b it (d B )
31
Medium Access Control (MAC)
• Controls who gets to transmit when
• Avoids “collisions” of packet
transmissions
32
Coordination Problem
33
Collisions
RReece
ceive
iver r
RReece
ceive
iver r
S ta tio n 1
S ta tio n 1
S ta tio n m
S ta tio n 2
S ta tio n 2
Receiver electronics detects collision
S ta tio n m
S ta tio n 2
S ta tio n 2
Receiver broadcasts info about collision (jam)
пЃў = total time to detect collision = RTT of the most distant station
34
Channel State
Assumption:
There is always at least one station in need of transmission
Id le
S u cce ssfu l
tra n sm ission
E rro r/C o llisio n
T im e
Objective:
Maximize the fraction of time for the “Successful transmission” state
( or: minimize the duration of “Idle” and “Collision” )
35
MUX
Multiaccess vs. Multiplexing
Ordering of packets
on higher capacity link
Receiver
Ordering of packets
on shared medium
36
Deterministic Schemes
FDM A
fre q u e n cy
fre q u e n cy
TDM A
1 2 3
m 1 2 3
m 1 2 3
m
m
m
m
3
2
1
3
2
1
3
2
1
tim e
tim e
Static multiaccess schemes: TDMA and FDMA
37
p e rc e n t o f o c c u rre n c e s (% )
Poisson Arrivals Model
20
15
10
5
0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
a rriv a ls p e r tim e u n it (n )
38
Parameter пЃў
• Ratio of propagation delay vs. packet
transmission time
txmit
txmit
Transmitter
t
Receiver
t
пЃґ
пЃў<1
пЃўВ»1
Propagation constant пЃў :
пЃў пЂЅ
пЃґ
пЃґ
t xm it
пЂЅ
пЃґC
L
39
Vulnerable Period
• Packet will not suffer collision if no other
packets are sent within one packet time
of its start
Collides with
the head of the
current packet
Current packet
Collides with
the tail of the
current packet
tstart
Vulnerable period
tstart пЂ­ txmit
Time
tstart пЂ« txmit
40
ALOHA Protocols
ALOHA
Packet
Arrivals
1
Departures
Slotted
ALOHA
Packet
Arrivals
Departures
2
1
3
2
1
2
1
4
3
3
5
4
4
2
6
5
5
3
6
6
4
7
Time
7
7
Time
5
41
Transmission Success Rate
Arrivals at
Station 1
Departures
Time
Time
Slot 1
Slot 2
Slot 3
Slot 4
Packet
Time
1
Receiver
k
Arrivals at
Station k
Departures
Slot 1
Slot 2
Slot 3
(a) – Slotted ALOHA
Slot 4
Time
Time
(b) – Pure ALOHA
42
ALOHA and Slotted ALOHA
State Diagram
W a it fo r
b a cko ff
S -A L O H A
ALO HA
B a cko ff п‚Ј C W m a x /
In cre a se
b a cko ff
B a cko ff пЂѕ C W m a x /
A b o rt
C o llisio n /
W a it fo r
sta rt o f slo t
Send
S -A L O H A
ALO HA
W a it fo r
ACK
A C K a rrive d /
End
43
Analysis of Slotted ALOHA (1)
ASSUMPTIONS FOR ANALYSIS:
• All packets require 1 slot for x-mit
• Poisson arrivals, arrival rate 
• Collision or perfect reception (no errors)
• Immediate feedback (0, 1, e)
• Retransmission of collisions
(backlogged stations)
• No buffering or infinite set of stations
Time Slots
(m = п‚Ґ)
iпЂ­1
i
iпЂ«1
iпЂ«2
44
Backlogged Stations
• “Fresh” stations transmit new
packets
• “Backlogged” stations re-transmit
collided packets
RReece
ceive
iver r
“F re sh ” sta tio n
“B a cklo g g e d ” sta tion
пЃ¬ /m
F re sh S ta tio n
пЃ¬ /m
B a cklo g g e d S ta tio n
45
ALOHA System Model (1)
• In equilibrium state, system
input equals system output
пЃ¬ = S = GeпЂ­G
S y s te m O u tp u t = S
“F re sh ” s ta tio n
S y s te m
RReece
ceive
iver r
“B a ck lo g g e d ” s ta tion
T ra n s m is sio n A tte m p ts = G
пЃ¬ /m
пЃ¬ /m
пЃ¬ /m
пЃ¬ /m
S y s te m In p u t = пЃ¬
46
ALOHA System Model (2)
G пѓ—P 0
G
пЃ¬
C hannel
S
G пѓ—(1 пЂ­ P 0 )
47
Analysis of Slotted ALOHA (2)
• 0 <  < 1, since at most 1 packet / slot
• Equilibrium: departure rate = arrival rate
• Backlogged stations transmit randomly
• Retransmissions + new transmissions:
Poisson process with parameter G > пЃ¬
• The probability of successful x-mit: S=GP0,
where P0=prob. packet avoids collision
• No collision => no other packets in the same slot:
S пЂЅ GP 0 пЂЅ G п‚ґ P пЃ»A ( t пЂ« 1) пЂ­ A ( t ) пЂЅ 0пЃЅ пЂЅ Ge
пЂ­G
48
S (th ro u g h p u t p e r p a cke t tim e )
Efficiency of ALOHA’s
E q u ilib riu m
0 .4
S lo tte d A L O H A : S = G e – G
0 .3
A rriv a l ra te пЃ¬
0 .2
P u re A L O H A : S = G e – 2 G
0 .1
0
0 .5
1 .0
1 .5
2 .0
3 .0
G (tra n s m is sio n a tte m p ts p e r p a c k e t tim e )
S-ALOHA: In equilibrium, arrival rate = departure rate:
пЃ¬ = GeпЂ­G
Max departure rate (throughput) = 1/e п‚» 0.368 @ G49 = 1
Unslotted (Pure) ALOHA
• Assume: all packets same size, but no
fixed slots
• The packet suffers no collision if no
other packet is sent within 2 packets
long: S=GP0=GeпЂ­2G
• Max throughput 1/2e  0.184 @ G = 0.5
• Less efficient than S-ALOHA, but
simpler, no global time synchronization
i
50
Markov chain for S-ALOHA
P 02
P 12
0
1
P 10
P 00
P 23
2
P 21
P 11
P 04
P 03
3
4
P 33
P 44
P 32
P 22
51
Instability of Slotted ALOHA
N e g a tive d rift
S (th ro u g h p u t p e r slo t)
D e sire d
sta b le
p o in t
P o sitive d rift
D e p a rtu re ra te
G пѓ—e пЂ­ G
m пѓ—q a
U n sta b le
e q u ilib riu m
U n d e sire d
sta b le
p o in t
A rriva l ra te
(m пЂ­ n ) пѓ— q a
n = 0
G = 0
G = (m пЂ­ n ) пѓ— q a пЂ« n пѓ— q r
G = m пѓ—q a
n = m
G = m пѓ—q r
G (tra n sm issio n a tte m p ts p e r slo t)
52
Carrier Sensing (CSMA)
• Listen before talk (unlike ALOHA,
where talk when you need to)
53
CSMA/CD
1. Wait until the channel is idle.
2. When the channel is idle, transmit
immediately and listen while
transmitting.
3. In case of a collision, stop the packet
transmission, and then wait for a
random delay and go to step 1.
IEEE 802.3 (Ethernet)
54
Basic CSMA Protocols
CSMA
Protocol
Transmission Rules
Nonpersistent
If medium is idle, transmit.
If medium is busy, wait random amount of time
and sense channel again.
1-persistent
If medium is idle, transmit.
If medium is busy, continue sensing until
channel is idle;
then transmit immediately.
p-persistent
If medium is idle, transmit with probability p.
If medium is busy, continue sensing until
channel is idle;
then transmit with probability p.
55
CSMA Protocols State Diagram
W a it
1 slo t
Id le (p -p e rsiste n t)
P r(1 -p ) /
T im e o u t
(C S M A /C A ) /
Id le (p -p e rsiste n t)
P r(p ) /
W a it fo r
b a cko ff
A C K re ce ive d
(C S M A /C A ) /
Id le (1 -p e rsiste n t
& n o n p e rsiste n t) /
S e n se
Send
Id le
(C S M A /C A ) /
B u sy (1 -p e rsiste n t
& p -p e rsiste n t) /
W a it
ra n d o m
tim e
End
N o C o llisio n
(C S M A /C D ) /
B a cko ff O K /
In cre a se
b a cko ff
B a cko ff
to o la rg e /
W a it fo r
IF S
B u sy
(n o n p e rsiste n t) /
C o llisio n
(C S M A /C D ) /
Ja m
A b o rt
56
Nonpersistent CSMA
Id le
p e rio d
1
P a cke t A
1
T im e
P a cke t B
S ta tio n 1
пЃў
S ta tio n 2
1
P a cke t C
S ta tio n 3
Y
V u ln e ra b le
p e rio d пЃў
пЃў
V u ln e ra b le
p e rio d пЃў
S ta tio n m
0
1
1пЂ«пЃў
S u cce ssfu l tra n sm issio n
(p e rio d = 1 пЂ« пЃў )
C o llisio n
(p e rio d = 1 + Y пЂ« пЃў )
57
(a)
T h ro u g h p u t p e r slo t tim e
Efficiency of CSMA protocols
g e пЂ­g
1
пЃў пЂ« 1 пЂ­ e пЂ­g
1 пЂ« пѓ–2пЃў
D e p a rtu re ra te
пЃ¬
A rriva l ra te пЃ¬
E q u ilib riu m
g = пѓ– (2 пЃў )
g (tra n sm issio n a tte m p ts p e r slo t tim e )
(b)
S (th ro u g h p u t p e r p a ck e t tim e )
1 .0
N o n p e rs is te n t
CSMA
0 .8
N o n p e rs is te n t
C S M A /C D
пЃў = 0 .0 1
0 .6
1 -p e rs iste n t C S M A
0 .4
0 .2
S lo tte d
ALO H A
P u re A L O H A
0 .1
1
10
100
G (tra n s m is s io n a tte m p ts p e r p a c k e t tim e )
1000
58
A ve ra g e p a cke t d e la y
TDM A
CSMA
M a xim u m ch a n n e l
tra n sm issio n ra te
Delay vs. Arrival Rate
ALO HA
A rriv a l ra te пЃ¬
59
Hidden and Exposed
Terminals
Range of A’s
transmissions
Range of B’s transmissions
B
A
B
C
Hidden Terminal
A
D
C
Exposed Terminal
60
CSMA/Basic Atomic Exchange
Id le co n te n tio n
p e rio d
T im e
D a ta P a cke t
Busy
Sender
IF S
(2 пЃў )
Busy
R e ce ive r
V u ln e ra b le
p e rio d = пЃў
Busy
C o ve re d S ta tio n
A cce ss to m e d iu m d e fe rre d
Busy
V u ln e ra b le p e rio d = P a cke t tim e
H id d e n S ta tio n
61
CSMA/MACA Atomic Exchange
Idle contention
period
Busy
Time
RTS
Data Packet
Sender
IFS
(2пЃў)
IFS
IFS
CTS
Busy
Receiver
Vulnerable
period = пЃў
Busy
Covered Station
Vulnerable period
= RTS + IFS + пЃў
Access to medium deferred
Busy
Hidden Station
Access to medium deferred
62
RTS/CTS Exchange (1)
R T S (N -b yte s)
B
A
C
63
RTS/CTS Exchange (2)
B
A
C
C T S (N -b yte s)
64
RTS/CTS Exchange (3)
N -b yte s P a cke t
B
A
C
D e fe r(N -b yte s)
65
Components of 802.11 LANs
Ad hoc network does not have distribution system nor access point
66
IBSS and Infrastructure BSS
Independent BSS (IBSS)
Infrastructure BSS
67
Extended Service Set (ESS)
DS
AP1
BSS1
AP2
BSS2
t= 1
AP3
BSS3
t= 2
68
802.11 Network Services
Service
Provider
Description
Distribution
Distribution
Service used by stations to exchange MAC frames when the frame
must traverse the DS to get from a station in one BSS to a station in
another BSS.
Integration
Distribution
Frame delivery to an IEEE 802 LAN outside the wireless network.
Association
Distribution
Used to establish a logical connection between a mobile station and an
AP. This connection is necessary in order for the DS to know where
and how to deliver data to the mobile station.
Reassociation
Distribution
Enables an established association to be transferred from one AP to
another, allowing a mobile station to move from one BSS to another.
Disassociation
Distribution
Removes the wireless station from the network.
Authentication
Station
Establishes identity prior to establishing association.
Deauthentication
Station
Used to terminate authentication, and by extension, association.
Privacy
Station
Provides protection against eavesdropping.
MSDU delivery
Station
Delivers data to the recipient.
69
States and Services
D e -a u th e n tica tio n
N o tifica tio n
S ta te 1 :
U n a u th e n tic a te d ,
U n a ss o c ia te d
D is a s so c ia tio n
N o tifica tio n
S ta te 2 :
A u th e n tica te d ,
U n a ss o c ia te d
S u c c e ss fu l
A u th e n tica tio n
D e -a u th e n tica tio n
N o tifica tio n
C la s s 1
F ra m e s
C la s s 1 & 2
F ra m e s
S ta te 3 :
A u th e n tica te d
a n d A s s o c ia te d
S u c c e ss fu l
A u th e n tica tio n o r
R e -a s so cia tio n
C la s s 1 , 2 & 3
F ra m e s
70
802.11 Interframe Spacings
D IF S
P IF S
S IF S
B u sy
C o n te n tio n
p e rio d
.....
F ra m e tra n sm issio n
B a cko ff
slo ts
D e fe r a cce ss
T im e
S e le ct slo t u sin g b in a ry e xp o n e n tia l b a cko ff
71
Basic 802.11 Transmission Mode
B a cko ff
Sender
Busy
T im e
D a ta
Busy
4 3 2 1 0
S IF S
D IF S
ACK
R e ce ive r
72
N e w p a cke t /
802.11 Protocol State Diagram –
Sender
Id le /
S e n se
W a it fo r
D IF S
Id le /
A C K e rro r-fre e /
S e n se
Send
End
A C K in e rro r /
B u sy /
B u sy /
W a it fo r
E IF S
T im e o u t /
1
In cre a se C W &
R e try co u n t
R e try пЂѕ R e try m a x /
A b o rt
R e try п‚Ј R e try m a x /
1
B a cko ff = = 0 /
W a it fo r e n d o f
tra n sm issio n
W a it fo r
IF S
Id le /
S e n se
B u sy /
Set
B a cko ff
1
C o u n td o w n fo r b a cko ff
w h ile m e d iu m id le
B a cko ff пЂѕ 0 /
73
802.11 Protocol State Diagram –
Receiver
P a cke t e rro r-fre e /
R e ce ive
W a it fo r
S IF S
Send
ACK
End
P a cke t in e rro r /
W a it fo r
E IF S
74
Example: Infra BSS
S ta tio n A
D a ta
S IF S
D IF S
S IF S
Assume Station A has a single packet to transmit to B
D IF S
T im e
E xa m p le : b a cko ff = 4
ACK
AP
S ta tio n B
D a ta
4 ,3 ,2 ,1 ,0
ACK
75
Timing Diagrams
Timing of successful frame transmissions under the DCF.
(a)
P a cke t a rriva l,
ch a n n e l id le
D IF S
D IF S
F ra m e
B a cko ff
T im e
F ra m e
ACK
N o b a cko ff
(b)
B u sy
B u sy
S IF S
D IF S
E IF S
B a cko ff
F ra m e
Frame retransmission due to ACK failure.
(c)
ACK
S IF S
B a cko ff
F ra m e
ACK
ACK
S IF S
D IF S
S IF S
A C K T im e o u t
B a cko ff
F ra m e
Frame retransmission due to an erroneous data frame reception.
B a cko ff
F ra m e
ACK
S IF S
76
5 4 3 2 1 0
3 2 1 0
7 6 5 4 3 2 1 0
D IF S
F ra m e *
D IF S
CP
D IF S
F ra m e *
D IF S
STA 1
D IF S
Backoff Mechanism
4 3 2 1 0
R e m a in d e r B a cko ff
STA 2
F ra m e *
9 8 7 6 5 4 3 2 1 0
7 6 5 4 3 2 1 0
CP
STA 3
4 3 2 1 0
2 1 0
CP
CP
F ra m e *
1 0
F ra m e *
4 3 2 1 0
3 2 1 0
4 3 2 1 0
The backoff mechanism of 802.11 MAC.
The Frame* transmission time includes the RTS/CTS exchange and the MAC layer ACK.
CP: Contention period.
77
D IF S
S IF S
RTS/CTS Transmission Mode
B a cko ff
RTS
Busy
T im e
D a ta
S IF S
Busy
S IF S
4 3 2 1 0
Sender
CTS
ACK
R e ce ive r
N A V (D a ta )
N A V (C T S )
D IF S
B a cko ff
N A V (R T S )
Busy
C o ve re d S ta tio n
D IF S
8 7 6 5 4
B a cko ff
A cce ss to m e d iu m d e fe rre d
Busy
H id d e n S ta tio n
A cce ss to m e d iu m d e fe rre d
78
802.11 MAC Frame Format
b yte s
2
2
6
FFCC DD/I/I
6
AAddddre
ress
ss
AAddddre
ress
ss
6
2
AAddddre
ress
ss SSCC
6
0 to 2 3 1 2
4
AAddddre
ressss
FFra
rammee bbooddyy
FFCCSS
F C = F ra m e co n tro l
D /I = D u ra tio n /C o n n e ctio n ID
S C = S e q u e n ce co n tro l
F C S = F ra m e ch e ck se q u e n ce
b its
2
PPro
rototoco
col l
ve
versio
rsionn
DS
MF
RT
PM
2
TTyp
ypee
= D istrib u tio n syste m
= M o re fra g m e n ts
= R e try
= Pow er m anagem ent
4
1
SSuubbtyp
typee
1
1
1
1
1
TToo FFro
romm MMFF RRTT PPMM MMDD
DDSS DDSS
1
1
W
W
OO
M D = M o re d a ta
W = W ire d e q u iva le n t p riva cy (W E P ) b it
O = O rd e r
79
802.11 Performance Analysis
пЃ¬ A ppl
STA 1
пЃ¬ A ppl
пЃ¬ A ppl
2
r
m
r
пЃ¬c
r
C h ann e l
80
C hannel
sta te
Id le
In te r-e ve n t
e lig ib le p e rio d 1
Busy
B a cko ff
D IF S
ACK
D IF S
7 6 5 4 3
Id le
In te r-e ve n t
e lig ib le p e rio d 2 a
E ve n t 4 : P a cke t 2
tra n sm issio n
B cko f
R T S D IF S
3 2 1 0
Busy
Id le
E ve n t 5 : P a cke t 2
re -tra n sm issio n
Bsy
In te r-e ve n t
e lig ib le p e rio d 2 b
B a cko ff
RTS
4 3 2 1 0
Id le
CTS
S IF S
CTS
D a ta
A n o th e r sta tio n
tra n sm its
S IF S
RTS
S IF S
B a cko ff
5 4 3 2 1 0
Busy
E ve n t 3 :
P a cke t 2 a rriva l
S IF S
D IF S
E ve n t 2 : P a cke t 1
tra n sm issio n
S IF S
E ve n t 1 :
P a cke t 1 a rriva l
Busy
In te r-e ve n t
e lig ib le p e rio d 3
81
D a ta
T im e
Transmission Example
B u s y/s u c c e s s
A ctu a l ch a n n e l sta te
o b se rve d b y A P
Id le
C h a n n e l sta te
o b se rve d b y A
RTS
S IF S
CTS
S IF S
D a ta
B u s y/c o llis io n
S IF S
ACK
Id le
Id le
Busy
tra n sm it
a tte m p t
Id le
D IF S
Busy
12 11 10 9
RTS
RTS
Id le
8
7
6
D IF S
Busy
6
5
4
3
2
D IF S
2
1
82
p id le
~
p s u c c пѓ—p id le
~
p s u c c пѓ—p id le
K = пЂ­1
C = 0
~
~
(p
s u c c пѓ—p b u s y пЂ« p c o ll )/ C W (0 )
~
p s u c c пѓ—p b u s y / C W (0 )
~
p s u c c пѓ—p b u s y / C W (0 )
K = 0
C = 0
p id le
C W (1 )
K = 1
C = 0
0
1
p id le
1
1
0
C W (0 )
p busy
~
p c o ll
C W (1 )
p id le
p id le
p busy
1
C W (1 )
p busy
~
p c o ll
C W (2 )
C W (2 )
~
p c o ll
~
p c o ll
C W (5 )
C W (5 )
C W (5 )
K = 5
C = 0
p id le
C W (1 )
~
p c o ll
~
p c o ll
p id le
p busy
~
p c o ll
~
p c o ll
~
p succ
p b u s y / C W (0 )
p id le
5
1
p id le
p id le
p busy
1
p busy
~
p c o ll
~
p c o ll
~
p c o ll
C W (5 )
C W (5 )
C W (5 )
K = пЃ¬
C = 0
5
C W (5 )
p id le
пЃ¬
1
p busy
p id le
p id le
пЃ¬
C W (5 )
p busy
83
802.11 Protocol Architecture
802.11 MAC
802.11
FHSS
802.11
DSSS
802.11a
OFDM
802.11b
DSSS
84
802.11 PHY Frame Using DSSS
P L C P p ream b le
P L C P h ea de r
S F D (16 b its)
S yn ch ron ization (128b its)
S ignal (8 b its)
H E C (16 b its)
Length (16 b its)
P a yload
(va riab le )
S e rvice (8 b its)
85
IEEE 802.11b BER vs. SNR
1 0 пЂ­1
1 0 пЂ­2
C C K 11
C C K 5 .5
BER
1 0 пЂ­3
DQPSK
1 0 пЂ­4
DBPSK
1 0 пЂ­5
1 0 пЂ­6
пЂ­10
пЂ­5
0
5
S N R (d B )
10
86
IEEE 802.11b Throughput vs.
SNR
7
CCK 11
T h ro u g h p u t (M b p s)
6
5
C C K 5 .5
4
3
2
DQPSK
DBPSK
1
0
пЂ­5
0
5
S N R (d B )
10
15
20
87
W-LAN Transmission Rates
1M bps
DBPSK
2M bps
DQPSK
11M bps
400 m
270 m
160 m
D Q P S K /C C K
D B P S K /C C K
5 .5 M b p s
550 m
A cce ss P o in t
M o b ile N o d e
O b sta cle
11 Mbps пѓ› 8 % of coverage area
1 Mbps пѓ› 47 % of coverage area
Lucent ORiNICO 802.11b
outdoors, no obstruction—ideal conditions!
пѓћ Low probability of having good link!!
88
Asymmetry
пѓ–3
A cce ss P o in t T ra n sm issio n R a n g e
A cce ss P o in t H e a rin g R a n g e
AP
A
1
B
89
Receiver-Based Autorate MAC
Protocol
R TS at 2 M bps
C TS at 1 M bps
1: RTS
B
A
2: CTS
D
D a ta a t 1 M b p s
C
3 : D a ta
N A V u p d a te d u sin g ra te
sp e cifie d in th e d a ta p a cke t
90
2 .4 G H z
1 1 : 2 .4 6 2
1 0 : 2 .4 5 7
9 : 2 .4 5 2
8 : 2 .4 4 7
7 : 2 .4 4 2
6 : 2 .4 3 7
5 : 2 .4 3 2
4 : 2 .4 2 7
3 : 2 .4 2 2
2 : 2 .4 1 7
1 : 2 .4 1 2
IEEE 802.11b Channels
5 MHz
22 M Hz
NOTE: The 12 channels in 802.11a do NOT overlap
2 .4 8 3 G H z
91
Power Conservation
92
Comparison of 802.11’s
Standard
802.11a
Number of channels
п‚ґ
Interference
п‚ґ
Bandwidth
п‚ґ
802.11b
802.11g
п‚ґ
Power consumption
п‚ґ
п‚ґ
Range/penetration
п‚ґ
п‚ґ
п‚ґ
Upgrade/compatibility
Price
п‚ґ
п‚ґ
http://www.nwfusion.com/techinsider/2002/0520wlan/0520feat1.html
93
Route Discovery in DSR (1)
D
C
Y
E
G
I
F
B
A
K
Z
H
L
J
94
Route Discovery in DSR (2)
R R E Q [C ]
D
Y
C
E
G
R R E Q [C ]
I
F
B
A
K
Z
H
L
J
Broadcast Tx
Represents a node that has received RREQ for H from C
95
Route Discovery in DSR (3)
D
C
Y
E
G
R R E Q [C , E ]
I
F
B
Z
H
R R E Q [C , B ]
A
K
L
J
96
Route Discovery in DSR (4)
D
Y
C
E
G
R R E Q [C , E , G ]
I
F
B
Z
H
R R E Q [C , B , A ]
R R E Q [C , B , A ]
A
K
L
J
97
Route Discovery in DSR (5)
D
C
Y
E
G
R R E P [C , E , G , H ]
I
F
B
Z
H
R R E Q [C , B , A , K ]
A
K
L
J
98
Route Discovery in AODV (1)
D
C
E
G
I
F
B
A
K
H
L
J
99
Multihop Throughput
Challenge: more hops, less throughput
Links in route share radio spectrum
Extra hops reduce throughput
Throughput = 1
Throughput = 1/2
Throughput = 1/3
100
Cellular Hierarchy
S a te llite
R e g io n a l A re a
L o w -tie r
H ig h -tie r
L o c a l A re a
W id e A re a
H ig h M o b ility
L o w M o b ility
101
Hybrid Wireless Networks
Infrastructure + MANET
A cce ss P o in t
M o b ile N o d e
O b sta cle
(a)
(b)
(c)
102
Community Mesh Network
W iM A X
Tower
In te rn e t
C a b le
O p e ra to r
C e n tra l
O ffice
F ib e r B a ckb o n e
W iM A X
C a b le N e tw o rk
DSL
M e sh N e tw o rk
103
Документ
Категория
Презентации
Просмотров
4
Размер файла
4 211 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа