Lecture 9: Wireless Networks Anders Västberg 08-790 44 55 [email protected].
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Transcript of Lecture 9: Wireless Networks Anders Västberg 08-790 44 55 [email protected].
Wireless Networks
• Provide fixed network access to a large number of stationary or mobile users.
• Examples:– Radio and television broadcasting systems– Mobile telephone systems (PSTN access)– Mobile broadband systems (Internet access)
Taxonomy of Wireless Networks
Wireless Networks
Fixed NetworksMobile Access
NetworksAd Hoc Networks
Cellular NetworksRandom Acess
NetworksMultihop Wireless
InternetsSensor Networks
[Kumar et al., 2004]
Duplex Communication
• Downlink: Communication from the BS to the MT.
• Upplink: Communication from the MT to the BS.
• Multiplexed by – Frequency Division Duplex (FDD)– Time Division Duplex (TDD)
Cellular System Overview
[Stallings, 2005]
Radio Access Ports (RAP)
• Provides Wireless Connections to Mobile Terminal (MT)
• Service area
• Coverage area
• Area availability
• Population availability
Capacity
• System capacity– Maximum number of users that can be served– Given a certain quality level
• Blocking probability
Range/Interference
• Few RAP, Low user densities =>Range limited systems
• Many RAP and user terminals =>Interference limited systems
Reuse distance
0 500 1000 1500 2000 2500 3000
140
130
120
110
100
90
80
D
R R
tt
dBW
Capacity
• Reuse distance
• Capacity only dependent on the ration between resuse distance and cell radius
• The system is scalable
Cell GeometryTesselation
[Stallings, 2005]
Frequency Reuse
Fixed Channel Allocation
K
C
KR
D3
,...3,2,1,0,22 jijijiK
}21,19,16,13,12,9,7,4,3,1{K
Capacity (channels/cell)
Normalized resuse distance
Cluster size
cA A
Area Capacity (channels/a.u.)
Worst Case Downlink Scenario
[Ahlin et al., 2006]
Worst Case Uplink Scenario
[Ahlin et al., 2006]
Capacity increase
• Adding new channels– Increase C
• New modulation and coding schemes– Decrease t
• Smaller Cells– Decrease Ac
– Cell splitting
• Divide cells into sectors– Use directional antennas
Directional Antennas
2/1
2/2
)(
hh
hh
A
S
Ideal sector antenna
If main lobe is
Nh
2 the Interference power is reduced by a factor of N
