Wireless Technologies
1
Wireless LANs

14.2
We’ll start first with wireless LANs, then
move on to Bluetooth, followed by
wireless WANs
Note
A BSS without an AP is called an ad hoc
network;
a BSS with an AP is called an
infrastructure network.
14.3
Figure 14.1 Basic service sets (BSSs)
14.4
Figure 14.2 Extended service sets (ESSs)
14.5
WLAN Standards
802.11
Release Freq
Typ Throughput
Max Net Bitrate
----
1997
2.4 GHz
0.9 Mbps
2
IR/FHSS/DSSS
a
2003
5
23
54
OFDM
b
1999
2.4
4.3
11
DSSS
g
2003
2.4
19
54
OFDM
n
2009
2.4 / 5
74
600
OFDM
More on each of these a little later.
14.6
Mod
WLAN Performance (line rate)
WLAN Performance
60
Throughput (Mbps)
50
40
802.11g
30
20
802.11a
10
802.11b
0
0
100
200
300
400
Distance (ft)
Data Source: Cisco Networking Professional On-Line Live Tech Talk
7
500
Creating WLAN Connections



An Access Point (AP) broadcasts is SSID (service
set identifier) roughly every 100 ms and at 1
Mbps (to accommodate the slowest client)
The Wi-Fi standard leaves connection criteria
open to the client
The Wi-Fi spectrum is divided into a fixed
number of channels



14.8
11 in North America
13 in most of Europe and China
14 in Japan
Creating WLAN Connections



14.9
But not all channels are used due to the concern
of overlapping frequencies
In North America, only channels 1, 6 and 11 are
recommended for 802.11b and g.
IEEE 802.11a has 42 channels, of which only 24
are used in North America, from which only
about 12 are used to reduce overlapping
frequencies
Figure 14.3 MAC layers in IEEE 802.11 standard
FHSS - frequency hopping spread spectrum
DSSS - direct sequence spread spectrum
OFDM - orthogonal frequency division multiplexing
14.10
Figure 14.4 CSMA/CA flowchart
DIFS: distributed
interframe space
SIFS: short
interframe space
14.11
Figure 14.5 CSMA/CA and NAV (Network Allocation Vector)
When a station sends its RTS, it includes a time of how long it needs the medium.
Other stations then set their NAV timer to this time so they don’t transmit.
14.12 DIFS: Distributed interframe space; SIFS: short interframe space
Figure 14.6 Example of repetition interval
14.13
Figure 14.7 Frame format
FC: Frame Control
D: duration of the transmission that is used to set the value of NAV
SC: sequence control: defines the sequence number of the frame to be used in flow control
14.14
Table 14.1 Subfields in FC field
14.15
Figure 14.8 Control frames
FC: Frame Control
D: duration of the transmission that is used to set the value of NAV
14.16
Frame Types
Three types of frames:
1. Management - used for initial communication between
stations and access points
2. Control - used for accessing the channel (RTS) and
acknowledging frames (CTS or ACK) (See Figure 15-10).
3. Data - used for carrying data and control information
14.17
Table 14.2 Values of subfields in control frames
14.18
Table 14.3 Addresses
14.19
Case – 00 (ad hoc)
11-22-33-01-01-01
11-22-33-02-02-02
A1: 11-22-33-01-01-01
DA
A2: 11-22-33-02-02-02
SA
A3: BSS ID
A4: not used
20
Case – 01 (wired to wireless)
wireless
802.11
11-22-33-01-01-01
wired
802.3
99-88-77-09-09-09
A1 (RA): 11-22-33-01-01-01
A2 (TA): 99-88-77-09-09-09
11-22-33-02-02-02
DA: 11-22-33-01-01-01
SA: 11-22-33-02-02-02
A3 (SA): 11-22-33-02-02-02
A4: not used
RA: Wireless Receiver Address
TA: Wireless Transmitter Address
21
Case – 10 (wireless to wired)
wired
802.3
wireless
802.11
11-22-33-01-01-01
99-88-77-09-09-09
11-22-33-02-02-02
A1 (RA): 99-88-77-09-09-09
DA: 11-22-33-02-02-02
A2 (TA): 11-22-33-01-01-01
SA: 11-22-33-01-01-01
A3 (DA): 11-22-33-02-02-02
A4: not used
RA: Wireless Receiver Address
TA: Wireless Transmitter Address
22
Case – 11 (via wireless)
wired
802.3
11-22-33-01-01-01
wireless
802.11
99-88-77-09-09-09
DA: 11-22-33-02-02-02
SA: 11-22-33-01-01-01
wired
802.3
99-88-77-08-08-08
11-22-33-02-02-02
A1 (RA): 99-88-77-08-08-08
DA: 11-22-33-02-02-02
A2 (TA): 99-88-77-09-09-09
SA: 11-22-33-01-01-01
A3 (DA): 11-22-33-02-02-02
A4 (SA): 11-22-33-01-01-01
23
Figure 14.10 Hidden station problem
14.24
Note
The CTS frame in CSMA/CA handshake
can prevent collision from
a hidden station.
14.25
Wireless Bridge
Building A
Ethernet Backbone
Wireless
Bridge
Building B
Ethernet Backbone
Case 11
Wireless
Bridge
26
Wireless Repeater
LAN Backbone
Case 11
Wireless
repeater
Case 10
Case 01
27
Figure 14.11 Use of handshaking to prevent hidden station problem
Station C doesn’t hear RTS from B, but it does hear CTS
from A, so it knows something is up.
14.28
Figure 14.12 Exposed station problem
C wants to send to D, but hears A talking to B, so assumes
the medium is (incorrectly) busy.
14.29
Figure 14.13 Use of handshaking in exposed station problem
Looking for a CTS handshake does not work in this case.
14.30
Table 14.4 Physical layers
14.31
Figure 14.14 Industrial, scientific, and medical (ISM) band
14.32
IEEE 802.11b


First modification to the 802.11 standard
HR-DSSS (High Rate DSSS)


2.4 GHz (ISM band)




up to 14 (5MHz per channel)
Non-overlapping channel: 3
Speed: 1 (Baker), 2 (Baker), 5.5 (CCK), and 11M bps
(CCK)
Distance: 300 ft


2.412 – 2.484
Channel:


Baker code (chipping code) and Complementary Code Keying
(CCK)
In practice: ~100 ft
Interference: cordless phone, microwave oven
33
IEEE 802.11a


Higher speed protocol
5 GHz (UNII band)







5.15 – 5.825 GHz
Spread Spectrum Transmission: orthogonal
frequency division multiplexing (OFDM)
Data rate: 6, 9, 12, 18, 24, 36, 48, or 54Mbps
Mbps
Distance: ~60 ft
Less interference than 802.11b
More users per AP than 802.11b
More non-overlapping channels (8/12 vs. 3)
UNII: unlicensed national information infrastructure
34
IEEE 802.11g

Two competing standards to improve 802.11b





Frequency: 2.412 – 2.484G Hz (same as 802.11b)
Speed: up to 54M bps
Distance: comparable to 802.11b


Shorter distance at higher rate
Backward compatible with 802.11b


CCK => PBCC, 22M bps (This is known as 802.11b+)
DSSS => OFDM, 54M
Caveat: so is the performance.
Spread Spectrum Transmission: OFDM (same as
802.11a)
PBCC: Packet Binary Convolution Code
35
WLAN Performance
802.11b
802.11a
802.11g
Link Rate
(max)
UDP
11M bps
54M bps
54M bps
7.1M bps
30.5M bps
30.5M bps
TCP
5.9M bps
24.4M bps
24.4M bps
The test was conducted in a lab environment, and the distance is expected to be
less than 10m.
Ref. “WLAN Testing with IXIA IxChariot,” IXIA White Paper
36
802.11n





It is a standard – finally, but many pre-n
products
Over-the-air (OTA) data rate: 500 Mbps
MAC performance: 200 Mbps
Improved Channel bandwidth: 20MHz =>
40MHz
Physical layer: Multiple-Input-Multiple-Output
(MIMO)



An improvement over OFDM
Backward compatibility: 802.11g/a (2.4GHz,
and 5.0GHz)
Distance/coverage: somewhat shorter than
802.11g/a
37
MIMO
38
14-2 BLUETOOTH
Bluetooth is a wireless LAN technology designed to
connect devices of different functions such as
telephones, notebooks, computers, cameras, printers,
coffee makers, and so on. A Bluetooth LAN is an ad
hoc network, which means that the network is formed
spontaneously.
Topics discussed in this section:
Architecture
Bluetooth Layers
Baseband Layer
L2CAP
14.39
Figure 15.17
Bluetooth details
Radio layer - roughly equivalent to physical layer.
Uses 2.4 GHz ISM divided into 79 channels of 1 MHz each.
Uses FHSS: 1600 hops/sec, so each frequency lasts for
only 625 microseconds (1/1600). This is the dwell time.
Basic rate (BR) uses Gaussian FSK at 1 Mbps, extended data
rate (EDR) uses pi/4-DQPSK for 2 Mbps and 8DPSK for 3 Mbps
Baseband layer - roughly equivalent to MAC sublayer and
uses TDD-TDMA (time-division duplexing TDMA).
Similar to walkie-talkies using different carrier frequencies.
14.40
Figure 15.17
Bluetooth details
Primary-secondary architecture with up to 7 slaves in a piconet.
All devices share the primary’s clock.
Packet exchange based on two ticks of a 312.5 microsec clock.
14.41
Figure 14.19 Piconet
14.42
Figure 14.20 Scatternet
14.43
Figure 14.21
Bluetooth stack Windows CE 5.0
Required: L2CAP, SDP, LMP
L2CAP: Logical Link Control and
Adaptation Protocol – used to multiplex
multiple logical connections between two
devices
SDP: Service Discovery Protocol – allows a
device to discover services offered by other
devices
LMP: Link Management Protocol – used to
manage the radio link between 2 devices
14.44
Figure 14.22 Single-secondary communication
Note: primary transmits in even slots, secondary in odd
14.45
Figure 14.23 Multiple-secondary communication
14.46
Primary switches between secondaries in round-robin fashion
Figure 14.24 Frame format types
Access code: 72-bit field normally contains sync bits and ID of the primary to
distinguish the frame of one piconet from another
Address: up to 7 secondaries; 0 means broadcast
Type: defines the type of data coming from the upper layer
F: flow control (1 indicates buffer full); A: ACK (bluetooth uses stop and wait)
S: sequence number for stop and wait
14.47
Figure 14.25 L2CAP data packet format
L2CAP layer roughly equivalent to LLC layer in LANs
Length: length of data coming from upper layers
Channel ID: defines a unique ID for the virtual channel created at this level
14.48
Figure 16.1
16.49
Cellular system
Figure 16.2
16.50
Frequency reuse patterns
16.51
16.52
1G
2G
GSM
AMPS
D-AMPS
IS-136
CDMA
IS-95
iDEN
Nextel
2.5G
2.75G
GPRS
30-50 kbps
3G
UMTS
Wideband-CDMA
Wireless-CDMA
384kbps; AT&T,
T-Mobile
EDGE
75-135kbps
iPhone (1st
generation)
1xRTT
CDMA2000
1x
IS-2000
144 kbps
3.5G
CDMA2000
EV-DO
1xEV
EV
IS-856
2.5 Mbps down
154 kbps up
Verizon, Sprint
HSPA
LTE?
High speed
packet access
400-700kbps
(or 3G ?)
Long-term
Evolution
3-5 Mbps
CDMA2000
EV-DV
Dead?
3.1 Mbps down
1.8 Mbps up
UMB ??
UltraMobile
Broadband
WiMax??
EV-DO Rev.A
Up to 3.1Mbps
AT&T, Verizon, and Alltel now support LTE.
What about WiMax for 4G?
16.53
4G
Wi-Fi???
Note
AMPS is an analog cellular phone
system using FDMA.
16.54
Figure 16.3
16.55
Cellular bands for AMPS
Figure 16.4 AMPS reverse communication band
16.56
Figure 16.5 Second-generation cellular phone systems
16.57
Figure 16.6 D-AMPS
16.58
Note
D-AMPS, or IS-136, is a digital cellular
phone system using TDMA and FDMA.
16.59
Figure 16.7 GSM bands
16.60
Figure 16.8 GSM
GSM uses TDMA and FDMA concepts
GMSK (Gaussian minimum shift keying):
a form of FSK used in European systems
16.61
Figure 16.9 GSM Multiframe components
Lots of overhead!!
16.62
Figure 16.10 IS-95 CDMA forward (base to mobile) transmission
19.2 ksps = 19.2 kilosignals per second
19.2 ksps signal converted to 64-chip
sequence, giving 1.228 Mcps (mega-chips)
ESN: electronic serial
number of handset
ESN is used to generate 2^42 pseudorandom chips, each having
42 bits. Decimator chooses 1 bit out of the 64, and then is
scrambled with digitized voice to create privacy.
16.63
Figure 16.11 IS-95 CDMA reverse (mobile to base) transmission
Each 6 symbols are used to index into a 64x64 Walsh matrix; thus each 6-symbol chunk
is replaced (not multiplied as it would be with CDMA) with a 64-chip code.
A 42-bit unique code is generated by the mobile
hand set and combined with the 307.2 kcps signal
creating a 1.228 Mcps signal.
Note: CDMA not used here because no way of syncing all mobile devices together!
Frequency reuse is 1, since neighboring channels cannot interfere with CDMA or
DSSS transmission.
16.64
Note
In CDMA, one channel carries all
transmissions simultaneously.
12.65
Figure 12.23 Simple idea of communication with code
12.66
Figure 12.24 Chip sequences
12.67
Figure 12.25 Data representation in CDMA
12.68
Figure 12.26 Sharing channel in CDMA
12.69
Figure 12.27 Digital signal created by four stations in CDMA
12.70
Figure 12.28 Decoding of the composite signal for one in CDMA
12.71
Figure 12.29 General rule and examples of creating Walsh tables
12.72
Note
The number of sequences in a Walsh
table needs to be N = 2m.
12.73
Example 12.6
Find the chips for a network with
a. Two stations
b. Four stations
Solution
We can use the rows of W2 and W4 in Figure 12.29:
a. For a two-station network, we have
[+1 +1] and [+1 −1].
b. For a four-station network we have
[+1 +1 +1 +1], [+1 −1 +1 −1],
[+1 +1 −1 −1], and [+1 −1 −1 +1].
12.74
Example 12.7
What is the number of sequences if we have 90
stations in our network?
Solution
The number of sequences needs to be 2m. We need to
choose m = 7 and N = 27 or 128. We can then use 90
of the sequences as the chips.
12.75
Example 12.8
Prove that a receiving station can get the data sent by a
specific sender if it multiplies the entire data on the
channel by the sender’s chip code and then divides it by
the number of stations.
Solution
Let us prove this for the first station, using our previous
four-station example. We can say that the data on the
channel
D = (d1 ⋅ c1 + d2 ⋅ c2 + d3 ⋅ c3 + d4 ⋅ c4).
The receiver which wants to get the data sent by station 1
multiplies these data by c1.
12.76
Example 12.8 (continued)
When we divide the result by N, we get d1 .
12.77
2.5 Generation iDEN
iDEN (Integrated Dispatch
Enhanced Network)
• Functionally the same as MIRS
(Motorola Integrated Radio
System)
• A high-capacity digital trunked
radio system providing integrated
voice and data services to its
users
• Used by Nextel Communications
16.78
2.5 Generation GPRS
GPRS (General Packet Radio
Service)
• The 2.5G version of GSM
• Theoretically allows each user
access to 8 GSM data channels at
once, boosting data transfer speeds
to more than 100 Kbps (30 Kbps in
the real world since it only uses 2
GSM channels)
• AT&T Wireless, Cingular, T-Mobile
16.79
2.5 Generation 1xRTT
1xRTT (CDMA2000) 1x Radio
Transmission Technology
• The 2.5G backwards compatible
replacement for CDMA
• 1xRTT will replace CDMA and iDEN
• 1x means that it requires only the
same amount of spectrum as 2G
networks based on CDMA (IS-95)
•Sprint and Verizon
16.80
3rd Generation UMTS
UMTS (Universal Mobile
Telecommunications System)
• Also called Wideband CDMA
• The 3G version of GPRS
• UMTS is not backward compatible
with GSM, so first UMTS phones will
have to be dual-mode
• Based on TDMA, same as D-AMPS
and GSM
16.81
3rd Generation 1xEV
1xEV (1x Enhanced Version)
• The 3G replacement for 1xRTT
• Will come in two flavors
• 1xEV-DO for data only
• 1xEV-DV for data and voice
16.82
EDGE
EDGE (Enhanced Data rates
for Global Evolution)
• Further upgrade to GSM
• Possible 3G (no – 2.75G)
replacement for GPRS
• Uses improved modulation to triple
the data rate where reception is
clear
16.83
LTE
LTE (3GPP LTE – Long Term
Evolution)
• 3G upgrade to UMTS
• 3GPP – third generation partnership project
• LTE actually an architecture – contains EPS
(evolved packet system), EUTRAN (evolved
UTRAN), and EPC (evolved packet core)
•OFDM, QPSK, 16QAM, 64QAM, MIMO
16.84
16-2 SATELLITE NETWORKS
A satellite network is a combination of nodes, some of
which are satellites, that provides communication from
one point on the Earth to another. A node in the
network can be a satellite, an Earth station, or an enduser terminal or telephone.
Topics discussed in this section:
Orbits
Footprint
Three Categories of Satellites
GEO Satellites
MEO Satellites
LEO Satellites
16.85
Figure 16.13
16.86
Satellite orbits
Example 16.1
What is the period of the Moon, according to Kepler’s
law?
Here C is a constant approximately equal to 1/100. The
period is in seconds and the distance in kilometers.
16.87
Example 16.1 (continued)
Solution
The Moon is located approximately 384,000 km above the
Earth. The radius of the Earth is 6378 km. Applying the
formula, we get.
16.88
Example 16.2
According to Kepler’s law, what is the period of a satellite
that is located at an orbit approximately 35,786 km above
the Earth?
Solution
Applying the formula, we get
16.89
Example 16.2 (continued)
This means that a satellite located at 35,786 km has a
period of 24 h, which is the same as the rotation period of
the Earth. A satellite like this is said to be stationary to the
Earth. The orbit, as we will see, is called a
geosynchronous orbit.
16.90
Table 16.1
Satellite frequency bands
L: GPS
S: weather, NASA, Sirius/XM satellite radio
C: open satellite communications
Ku: popular with remote locations transmitting back to TV studio
Ka: communications satellites
16.91
Figure 16.15
16.92
Satellite orbit altitudes
Figure 16.16
Satellites in geostationary orbit
Rotate with the earth, usually over equator; 1/3 earth coverage
16.93
Figure 16.16
Example GEO satellite – Weather
Weather satellites can watch more than weather. Can also
observe city lights, fires, pollution effects, auroras, sand and
dust storms, snow cover, energy flows, volcano output, etc.
Can observe both visible spectrum and infrared spectrum
The U.S. has two geostationary weather birds: GOES-11 and
GOES-12. GOES-12, or GOES-EAST, over the Mississippi
River, covers most of the U.S. weather. GOES-11 covers the
eastern Pacific Ocean.
16.94
Figure 16.17 Orbits for typical LEO and MEO systems, e.g. GPS
LEO and MEO satellites need to move or their orbits will decay;
thus need >1 satellite to maintain connection.
16.95
Figure 16.18
Trilateration
In a 2D plane, two reference points yields 2 intersections, three
reference points yield 1 intersection
In a 3D plane, need four reference points to yield 1 intersection
16.96
Figure 16.19
LEO satellite systems
UML: user mobile link
GWL: gateway link
ISL: intersatellite link
16.97
Figure 16.20
LEO example: Iridium constellation
Designed by Motorola during the 1990s, went
bankrupt in 1999. What cost $5 billion was sold
for $25 million.
66 active satellites with a few spares at a height
of 781 km (485 miles).
Sold to Iridium Communications Inc.
Iridium plans to send up 66 new satellites and 6 spares
starting in 2015, called IridiumNext. Data and voice.
16.98
Figure 16.20
MEO example: GPS (global positioning system)
GPS was established in 1973 by U.S. and
consisted of 24 satellites (now ~32).
Dual-use system – military and civilian. Civilian
side used by commerce, science, banking, mobile
phones, farmers, surveyors, power grids, you and me.
GPS can provide absolute location, relative movement, and
time transfer.
Inducted into Space Foundation Space Technology Hall
of Fame in 1998.
Three satellites gives you 2 points, but you can choose the
one on the ground; 4 gives you 1 point and overcomes clock
errors; usually see at least 6; often see 8-10
16.99
Figure 16.20
MEO example: GPS (global positioning system)
Each satellite continually transmits messages
that include (1) the time the message was
transmitted, (2) precise orbital information (the
ephemeris), and (3) general system health and
rough orbits of all GPS satellites (the almanac)
Receiver takes messages, determines the transit time of each
message and computes the distances to each satellite.
These distances along with satellites’ locations are use
in determining receiver’s location (trilateration).
(See Wikipedia GPS for cool image of satellite visibility.)
16.100
Figure 16.20
MEO example: GPS (global positioning system)
GPS consists of 3 segments
(1) Space segment – the space vehicles at ~20,200km
(2) Control segment – a master control station, an alternate
master control station, four dedicated ground antennas, and
six dedicated monitor stations
(3) User segment – you and me
All satellites broadcast at two frequencies: 1.57542 GHz and
1.2276 GHz using CDMA spread-spectrum technology
What will you create?
16.101