BROADBAND CDMA

1
WLAN
2
Unlicensed Spectrum At 2.4 GHz
Maximum Power
1 watt

• The band can be used anywhere indoor or Outdoor
• The technology is designed for indoor. Its
  efficiency decreases with large delays

Indoor
Frequency
2.400
2.483 GHz
3
Unlicensed Spectrum At 5 GHz
1 watt
INDOOR/Outdoor
OUTDOOR
250 mw
INDOOR
50 mw
5.15
5.25
5.35
5.725
5.825 GHz
4
5 GHz Allocations in USA/Japan/Europe
5
Some Observations

• Free spectrum is a strong drive for private
  WLANs
• Security is the biggest worry of private WLANs
• Free spectrum could mean high interference
• WLANs are satisfying the need for Indoor
  Wireless Internet
• WLAN is trying to get OUTSIDE while 3G is trying
  to get INSIDE

6
IEEE802.11 Wireless LAN
Wired 802.3
Server
Router
Wireless 802.11
Portal
AP
AP
AP
7
Brief History of IEEE802.11
IEEE 802.11 e QoS
IEEE 802.11 b 5.5 / 11 Mbps
First complete standard from the IEEE802.11
committee
IEEE 802.11 i security
DS-SS
IEEE 802.11 g 22 Mbps
DS-SS
FH-SS
DS-SS
5 GHz IEEE 802.11 a 54 Mbps
FCC Allocated the 2.4 GHz Unlicensed Band
Slow Progress
Very Fast
OFDM
1988
1990
1992
1994
1996
1998
2000
8
IEEE 802.11 (First Version)
DS-CDMA

• Late in 1999 the IEEE 802.11 standard jumped from
  1 2 Mbps rate up to 11 Mbps
• Now most commercial systems offer a standard 11
  Mbps
• The Access is Direct Sequence CDMA

Fall 1999
9
Current IEEE802.11 Family of Standards
10
Channels of the 802.11b,g in 2.4 GHz
Only Three Non-Overlapping Channels
11
802.11 Channels
12
802.11a channel plan
13
802.11 Structure
Basic Service Set BSS
Independent BSS
Infrastructure BSS
14
Basic Service Set (BSS)

• Single cell
• Typically with Access Point (AP)
• BSS terminals AP A set of signaling rules

15
Extended Service Set ESS
Backbone Structure
AP
AP

• Multiple APs form what is known as ESS
• AP s periodically transmit beacons
• Wireless terminals scan and discover
• Authentication and association
• Adjacent AP s use different radio channels

16
802.11 Structure (continue)
17
Basic Operation

• Power ON
• Search for Beacon
• Acquire timing
• Initiate association
• Authentication
• Complete association
• Idle (power saving)

18
IEEE 802 Family

• The LLC layer is common to all 802 standards
• Several MAC and Physical standards share the same
  LLC 802.2

19
IEEE 802 Family continue

• The most common MAC is the normal ETHERNET which
  is known as Carrier Sense Multiple Access with
  collision detection CSMA/CD
• CSMA/CD is known as 802.3
• Other relevant 802 standards are
• 802.11 Wireless LAN
• 802.15 Wireless PAN
• 802.16 Wireless WAN
• 802.8 Fiber Optics
• 802.10 Network Security

20
Media Access Control (MAC)
Carrier Sense Multiple Access with Collision
Avoidance
CSMA/CA
Plus Back-Off Mechanism
FHSS Frequency-Hopped Spread Spectrum
DSSS Direct Sequence Spread Spectrum
OFDM Orthogonal Frequency Division Multiplexing
IR Infra Red
21
Basic Protocol
MAC
New Packet
Listen
N
N
Y
Idle?
Timed out?
Failed
Y
Back-off
Send RTS
Ready to Send
Upper Layers
N
CTS?
Clear to Send
N
Y
Y
ACK?
Send Data
Success
22
Efficient Wireless Operation

• Collision Avoidance
• Packet Interlacing
• Optional Fragmentation/Assembly at the MAC
• Power Saving Mode
• Enhanced Security

23
Packet Interlacing
A new packet can be sent while the current packet
is backed-off
24
Collision Avoidance
Collision Avoidance is used instead of the usual
Collision Detection
CTS
RTS
Tx
Rx
BSS
Tx Neighborhood
Rx Neighborhood
25
Accommodating Continuous Traffic

• Normal traffic must wait DIFS sec before
  contending for access
• The Access Point has privilege access at shorter
  time PIFS. It uses that access to poll real-time
  traffic
• The PIFS privilege is known as Point Coordination
  Function

26
WLAN Security
Wired Equivalent Privacy (WEP)

• Network Access Protection
• Authentication Password and Current key
• Eavesdropping
• The WEP Algorithm
• Pseudo Random Number Generator (PRNG) initialized
  by shared secret key
• Reasonably strong different PRNG for each frame
• Message-to-message self synchronization

27
802.11 Frame Structure
2
2
6
6
6
6
2
Frame Control
Duration
Address 1
Address 2
Address 3
Sequence
Address 4
MAC Header
Preamble for physical synchronization
Preamble
Header
MAC Header
Data
FCS
6
0-2312
physical Header
All lengths are given in Octets
1
1
1
2
28
Physical Preamble/Header
New All Standards
Old 1 2 Mbps Standard
29
Overview of Modulation/Coding
Old
Current
New
1 2 Mbps
Up to 11 Mbps
Up to 54 Mbps
FH-SS
DS-SS
DS-SS
PBCC QPSK/8PSK
CCK BPSK/QPSK
DS-SS
Barker Code BPSK/QPSK
PBCC BPSK/QPSK
OFDM
30
FH-SS
31
FH-SS (continue)
32
1 2 Mbps DS-SS
Data _at_ 1 Mbps
BPSK
BC
De-MUX
QPSK
11 MHz
BC
Data _at_ 2 Mbps





11-chip Barker Code (BC)
-
-
-
-
-
-
33
5.5 11 Mbps CCK DS-SS 802.11 b
34
802.11 b High Performance Option
PBCC Packet Binary Convolutional Code
11 MHz
35
Measured Attenuation at 2.4 GHz
36
Speed vs. Distance 802.11ab
Measured Performance of 5-GHz 802.11a Wireless
LAN Systems
By James C. Chen, Ph.D., Jeffrey M. Gilbert,
Ph.D., Atheros Communications, Inc. 529 Almanor
Ave. Sunnyvale, CA 94085 [phone]
www.atheros.com
37
Throughput vs. Distance TCP/IP/802.11ab
30
802.11 a
25
20
15
Throughput in Mbps
802.11 b
10
5
0
0
25
50
75
100
125
150
175
200
225
Range in Feet
38
Frequency Re-use
39
Throughput of 8-Cell System
30
802.11 a No CCI
25
802.11 b No CCI
20
15
Throughput in Mbps
802.11 b With CCI
10
5
0
0
25
50
75
100
125
Cell Radius in Feet
40
System Capacity vs. Coverage Area
41
802.11 version "a"

• The push for higher data rates
• Distortion and physical limitations
• Solution through OFDM modulation/Access
• 54 Mbps LANs based on OFDM physical layer
• Cost and performance of high speed 802.1
• Limitations of 802.11
• Interoperability between 802.11 and 1X-EV
  standard

42
802.11 version a

• When the required data speed is too high, the
  spread spectrum option becomes LESS attractive
• Invariably, these days, the alternative to SS is
  Orthogonal Frequency Division Multiplexing OFDM

43
Classic OFDM

• When the data rate is high, two problems arise
• There may not be room for spectrum spreading
• Distortion due to multipath distortion
• In OFDM, the data stream is split into many
  parallel streams, each of which is too slow to
  exhibit any significant multipath distortion

44
Basic OFDM Modulator
45
The OFDM Composite Spectrum
46
Modulating Each Sub-Carrier
47
Mapping Data Onto Sub-Carriers
48
Inverse Fourier Transform Implementation
49
Basic OFDM Receiver
50
Other OFDM Properties

• One OFDM channel could be shared by neighboring
  cells
• Offers the same flexibility as CDMA
• No theoretical limit on how many sub-channels
• Data can be increased as long as power is
  available
• Sensitive to non-linearity's
• Easy processing with FFTs

51
OFDM for IEEE802.11 a

• Number of sub-carriers N 52
• Number of Pilot sub-carriers 4
• Number of Data sub-carriers 48
• Bandwidth per subcarrier Df 300 kHz
• Total bandwidth 20 MHz
• Modulation methods
• BPSK / QPSK / 16QAM / 64QAM
• Coding 1/2 and 3/4
• Data rate per carrier 125 kbps to 1.5 Mbps

52
IEEE802.11a Frequency Plan
312.5 kHz
16.25 MHz
52 Carriers/channel
8 channels
GHz
5.150
5.180
5.200
5.220
5.240
5.260
5.280
5.300
5.320
5.350
53
What is WiMax?

• WiMax is an industrial forum that promotes
  deployments of Broadband Wireless Networks
• It supports IEEE801.16 family of standards
• Certify interoperability of products and
  technology
• Global drive for acceptance of broadband wireless

54
LOS Fresnel Zone
Wimax Optimized for non line of sight (NLOS)
coverage Up to 50 km LOS Up to 8 km NLOS
55
Why NLOS

• antenna height restrictions
• easier to install below the eaves)

56
What makes NLOS possible

• OFDM
• Sub-channelization
• Directional antennas
• Tx and rx diversity
• Adaptive modulation
• Error control coding
• Power control

57
Adaptive Modulation
58
IEEE802.16 Family
2 66 GHz Revision of 802.16 and
802.16a Compatibility to e
10 66 GHz WiMax System profiles
2 6 GHz Support for Mobile and Nomadic
computing
10 66 GHz Point-to-Point
2 11 GHz Point-to-Multi-Point Extension
802.16 REVd
802.16
802.16c
802.16a
802.16e
2001
2002
2003
2004
2005
59
Future Trends
60
Major Differences
WLAN
Cellular

• Designed for Indoor

• Designed for Outdoor

• Designed for Voice

• Designed for Data

61
Major Differences (continued)
WLAN
Cellular

• Unlicensed Bands

• Licensed Bands

Free Air

• Private Access

• Public Access

62
Trends in WLAN and Cellular Technologies
Cellular
W-LAN
W-LAN
63
Difficulties Facing Outdoor WLAN

• WLAN's access protocols are designed for small
  propagation delays

• Outdoor WLAN's is subjected to external
  interference

• Hard to convince wireless operator to build
  networks in an unlicensed band